Although nicotine is the major drug of abuse, little information is available on its sites and mechanism of action in the central nervous system. The proposed research is aimed at an understanding of the biochemical and pharmacologic parameters of the nicotine recognition site in rat brain as well its neuroanatomical distribution and functional significance. The specific aims are 1) to isolate and purify the nicotine recognition sites by affinity chromatography; 2) to examine their biochemical requirements and structure-activity relations employing a variety of nicotine analogues; 3) to prepare monoclonal antibodies to the purified binding sites; 4) to investigate the neuroanatomical localization of the nicotine recognition sites using immunocytochemical and autoradiographic techniques. A 3H-labeled affinity ligand will be used for in vivo labeling of the binding sites. Chronic binding and behavioral studies will be performed utilizing nicotine and mecamylamine, a nicotine antagonist. Nicotine analogues and related drugs will also be screened for their ability to antagonize the actions of nicotine in the brain. The studies may provide insight into the molecular mechanisms and sites of action of nicotine in the brain; and they may provide a therapeutic basis for dealing with the problem of tobacco smoking.